1. Field of the Invention
The invention is in the field of data monitoring and recording systems particularly adapted for use on vehicles.
2. Description of the Prior Art
Prior data recording apparatus has been utilized for recording various engine parameters for use as diagnostic and maintenance tools for land vehicles and aircraft. Additionally, recording devices have been utilized in connection with interstate truck travel to keep track of gasoline purchases in various states to take advantage of tax rebates and the like. Representative examples of these prior art devices as shown in U.S. Pat. Nos. 3,099,817; 3,964,302; 4,050,295; 3,864,731; 3,938,092; 3,702,989; and 3,792,445. Typically, these prior art devices utilize either singly or in combination various display means, manual input means, and recording means in the form of either paper or magnetic tape. In some instances only alarm indications are provided or pertinent data is displayed as shown, for example, in U.S. Pat. 4,050,295 and 3,964,302. In other cases entire vehicle performance data is recorded as discussed in U.S. Pat. No. 3,099,817. Attempts have been made to reduce the amount of recording and consequent tape usage by means of hardward and software selective data recording such as disclosed in U.S. Pat. Nos. 3,792,445 and 3,702,989.
A particular disadvantage of these prior art devices is their lack of versatility with regard to usage and recording of data and a reliance upon bulky and expensive magnetic or paper tape as a primary recording medium.
Of particular importance in utilizing data vehicle monitoring recording apparatus is the necessity to keep accurate track of time so that various malfunctioning engine parameters may be exactly correlated with the time of occurrence. Although various clocking techniques have been developed in the prior art, such as, for example, apparatus disclosed in U.S. Pat. Nos. 4,031,363, 4,022,017 and 3,889,461, these systems do not provide the necessary time tracking accuracy and reliability coupled with power conservation needs required in land vehicles. In particular, when a computing means such as a microprocessor is utilized to selectively filter and store data as well as provide a real time clock function there is a need for maintaining a high accuracy in the real time clock function despite inoperability of the microprocessor when the vehicle engine is turned off. In this connection the prior art has not addressed itself to the problem of shutting down the microprocessor in an orderly fashion to protect data being processed in the event of power failure or engine turnoff.